Diagnostic terminal problem

[alpineviking]

Greetings friends…

I have replaced injectors, fuel pumps, and upper engine wiring harness on my 93 400E. Afterwards, the engine runs perfectly in open loop, but runs like a lean condition In closed loop. I press the test button on the 8 pin diagnostic socket, and the LED light comes on. After releasing the button, there are no flashes, including the single flash for a good circuit.

At the 38 pin connector, no flash codes are present on circuit 19, which involves the LH injection, and there is no single flash for a good circuit. I replaced the “carb module” under the passenger side foot well, and there is still no flash for a good circuit. I substituted several LH injection modules without success.

At this point, I am suspecting that the replacement upper engine harness may be defective, but I have no idea whether or not the harness is carrying this circuit. I would appreciate any suggestions regarding the voltage source for the test light on the 8 pin diagnostic terminal or circuit 19 on the 38 pin connector.

Thanks!

 

[gsxr]

The built-in LED only shows codes from the DM (aka 'CARB module'). If your CEL is not on, there should be no codes on the DM. You will get the same codes (or, lack thereof) when checking pin 19 at the 38-pin diagnostic port. The test light/button at the 8 pin diagnostic terminal is in parallel (identical) to pin 19 on the 38 pin connector.

You need to check codes on all other modules, in particular LH and EZL if you are chasing what you think is a lean condition. You may also need live data if there are no codes present, and you can only get live data from SDS with HHT-Win, or (limited) live data from something like the Snap-On MT2500 with required cartridge/cable/keys.

If your upper harness has good insulation (late datecode), it's probably fine and completely unrelated to your issue. The harness connects to the injectors, MAF, and a few sensors. If the harness was defective you would likely have problems when cold / open loop.

Make sure to carefully read the HOW-TO which explains in detail checking codes on the 500E/400E.

Finally - what makes you so sure there is a lean condition? What are the exact symptoms? How old is the O2 sensor? Etc.

 

[alpineviking]

Thanks very much for the valuable input. I made an educated guess on the lean condition. It has a spotty idle and doesn’t produce smoke or act lethargic like a rich mixture. The O2 sensor is OEM Bosch and only has 500 miles on it. I am sure that the date code on the replacement harness is 2006.

I admit making a mistake while cleaning the MAF by using throttle body cleaner. I get the impression that this is certain failure of the unit. I will replace it with a spare, and see if it runs smoothly in closed loop.

This probably will not alleviate my lack of a report signal on socket 19 on the 38 pin port. Afterwards, I am taking the car to a local shop for a scan.

Thanks again for the info...

 

[gsxr]

I don't know if cleaning with throttle body cleaner will cause the MAF to completely fail. As a test you can drive the car with MAF disconnected. If it runs substantially better, the MAF could be defective. Note that running the engine with MAF unplugged will trigger false fault codes you will need to clear.

Note that for socket 19, the DM (CARB module) may not report any blink, instead of the usually-expected single blink. And, if your CEL is off, there should be no codes on the DM anyway. The DM only monitors for emissions-related faults and will not report other faults. This is why you must check the other powertrain computers separately for fault codes, per the HOW-TO that I mentioned previously.

If you pay a shop, make SURE they have an SDS with HHT-Win, but if you haven't cleared codes... you will likely get "code diarrhea" where a pile of old codes from years ago will still be present. I thought you already hade a hand-held code reader, if not, get one and use that first.